Have owned both the voigtlander pancakes at one point, but I gradually got tired of the lack of AF (I don't shoot static subjects and even with the 5DII's EG-S screen MFing can be a pain sometimes. It's no substitute for a split screen IMO)

When the 40mm EF came out I sold them both and bought the Canon. Build quality is not as good and the loss of a stop is a slight inconvenience, but the IQ is very good which is what matters for me.